Type Styles, Readability, and Legibility

In publication design there are two complementary concepts that drive many
typesetting choices: readability and legibility.
Readability is the quality of copy that makes it easy
to read in volume, for extended periods of time;
legibility refers to the ease with which data, words,
and short phrases can picked out while a passage is being scanned.

Styling for Readability

Our expectations of book design illuminate the definition of
readability:

Serif typefaces

12–15 words per line

Fully justified lines

Moderate and consistent letterspacing

Upmarket press runs also often employ increased leading (20% or
more of the body copy size) and more detailed fonts, to ease the task of
making out margins, lines, and letters. This is due to the fact that
profit margins on downmarket editions range from poor to outright lousy,
which creates a strong incentive to minimize manufacturing and
distribution costs—in other words, to reduce net paper costs.

In their turn, paper costs are reduced by using lower grades of
paper in smaller quantities. That being the case, there are more lines
on each page, smaller page margins, and—on account of paper quality—less-detailed fonts, which suffer
less from the ink bleeds that occur when lower grades of paper are
used.

Paper costs aren’t a concern on the Web, so we can use the full
arsenal of available tools to enhance readability. For screen display,
the result might be something like the following:

#bodycopy p { width: 50em; font-family: ...

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